1. Field of the Invention
The present invention relates to wireless communication, and more particularly, to a method and apparatus for receiving acknowledgement/not-acknowledgement (ACK/NACK) indicating a reception confirmation in a wireless communication system.
2. Related Art
One of the most important requirements of a next generation wireless communication system is to support a high data rate. For this, various techniques such as multiple input multiple output (MIMO), cooperative multiple point transmission (CoMP), relay, etc., have been under research, but the most fundamental and reliable solution is to increase a bandwidth.
However, a frequency resource is in a saturation state at present, and various schemes are partially used in a wide frequency band. For this reason, in order to ensure a broadband bandwidth to satisfy a required higher data rate, a system is designed such that a basic requirement which allows separate bands to operate respective independent systems is satisfied, and a carrier aggregation (CA) is introduced. In concept, the CA aggregates a plurality of bands into one system. In this case, a band that can be independently managed is defined as a component carrier (CC).
The latest communication standard (e.g., 3GPP LTE-A or 802.16m) considers to expand its bandwidth to 20 MHz or higher. In this case, a wideband is supported by aggregating one or more CCs. For example, if one CC corresponds to a bandwidth of 5 MHz, four carriers are aggregated to support a bandwidth of up to 20 MHz. As such, a system supporting carrier aggregation is called a carrier aggregation system.
Meanwhile, the wireless communication system considers a system in which more terminals are supported by one base station in comparison with the legacy system. For example, due to a technique such as machine type communication (MTC), enhanced multi user multi input multi output (MIMO), etc., there may be a need to support more terminals by one base station.
In this case, it may be difficult to transmit control information to multiple terminals when using only the conventional control channel for transmitting control information, for example, a physical downlink control channel (PDCCH) in long term evolution (LTE). This is because a problem may occur in which a radio resource of the PDCCH is not enough or an interference is severe. To solve such a problem, it is considered to allocate a new control channel in a radio resource region in which data is transmitted in the legacy system. Such a new control channel is called an enhanced-PDCCH (E-PDCCH). When using the E-PDCCH, how to determine a starting position of the E-PDCCH may be a matter to be considered.
Meanwhile, a base station transmits acknowledgement/not-acknowledgement (ACK/NACK) for uplink data received from the terminal through a physical hybrid-ARQ indicator channel (PHICH). The PHICH is located in a region to which a PDCCH, i.e., the legacy control channel, is allocated. The PHICH may also have a problem in which a radio resource is insufficient or an interference occurs if the number of terminals supported by the base station is increased and a carrier aggregation is supported. Therefore, it is considered to introduce a channel for new ACK/NACK transmission, and such a channel is called an enhanced-PHICH (E-PHICH).
Meanwhile, in a future wireless communication system, it is considered to use a carrier having a new channel structure which is not compatible with the legacy wireless communication system. Such a carrier is hereinafter called a new carrier type (NCT). A carrier used in the legacy wireless communication system is called a legacy carrier type (LCT). The future wireless communication system considers a carrier aggregation which aggregates the LCT and the NCT. In this case, how to determine a resource for transmitting ACK/NACK by a base station may be a matter to be considered.